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Title: ON SPECTRAL BREAKS IN THE POWER SPECTRA OF MAGNETIC FLUCTUATIONS IN FAST SOLAR WIND BETWEEN 0.3 AND 0.9 AU

Abstract

We analyze the radial variation of the power spectra of the magnetic field from 0.3 to about 0.9 AU, using Helios 2 spacecraft measurements in the fast solar wind. The time resolution of the magnetic field data allows us to study the power spectra up to 2 Hz. Generally, the corresponding spectral break frequency f{sub b} and the Doppler-shifted frequencies, which are related to the proton gyroradius and inertial scales, are close to a frequency f of about 0.5 Hz at a distance of 1 AU from the Sun. However, studying the radial evolution of the power spectra offers us the possibility to distinguish between those scales. Recent Ulysses observations show that, while the proton scales vary, f{sub b} stays nearly constant with the heliocentric distance R. In our study we confirm that f{sub b} varies within a small interval of [0.2, 0.4] Hz only, as R varies from 0.3 to 0.9 AU. Moreover, if we assume parallel propagating fluctuations (with respect to the solar wind flow or background magnetic field), we can show that none of the proton scales are coincident with the break scale. If, however, we take into account the two-dimensional nature of the turbulent fluctuations, thenmore » we can show that the spatial scale corresponding to f{sub b} (R) does follow the proton inertial scale, {lambda}{sub p}(R), but not the proton gyroradius scale, {rho}{sub p}(R), as a function of heliocentric distance. These observations indicate that the spectral break at the proton inertial scale might be related to the Hall effect, or be controlled by the ion-cyclotron damping of obliquely propagating fluctuations or the formation of current sheets scaling like {lambda}{sub p}, which could be responsible for ion heating through magnetic reconnection.« less

Authors:
;  [1]; ;  [2]
  1. Max-Planck-Institut fuer Sonnensystemforschung, 37191 Katlenburg-Lindau (Germany)
  2. LESIA, Observatoire de Paris, Meudon (France)
Publication Date:
OSTI Identifier:
22020436
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 749; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; DOPPLER EFFECT; HALL EFFECT; MAGNETIC FIELDS; MAGNETIC RECONNECTION; SOLAR PROTONS; SOLAR WIND; SUN; TIME RESOLUTION; TURBULENCE; TWO-DIMENSIONAL CALCULATIONS

Citation Formats

Bourouaine, S, Marsch, E, Alexandrova, O, and Maksimovic, M. ON SPECTRAL BREAKS IN THE POWER SPECTRA OF MAGNETIC FLUCTUATIONS IN FAST SOLAR WIND BETWEEN 0.3 AND 0.9 AU. United States: N. p., 2012. Web. doi:10.1088/0004-637X/749/2/102.
Bourouaine, S, Marsch, E, Alexandrova, O, & Maksimovic, M. ON SPECTRAL BREAKS IN THE POWER SPECTRA OF MAGNETIC FLUCTUATIONS IN FAST SOLAR WIND BETWEEN 0.3 AND 0.9 AU. United States. https://doi.org/10.1088/0004-637X/749/2/102
Bourouaine, S, Marsch, E, Alexandrova, O, and Maksimovic, M. 2012. "ON SPECTRAL BREAKS IN THE POWER SPECTRA OF MAGNETIC FLUCTUATIONS IN FAST SOLAR WIND BETWEEN 0.3 AND 0.9 AU". United States. https://doi.org/10.1088/0004-637X/749/2/102.
@article{osti_22020436,
title = {ON SPECTRAL BREAKS IN THE POWER SPECTRA OF MAGNETIC FLUCTUATIONS IN FAST SOLAR WIND BETWEEN 0.3 AND 0.9 AU},
author = {Bourouaine, S and Marsch, E and Alexandrova, O and Maksimovic, M},
abstractNote = {We analyze the radial variation of the power spectra of the magnetic field from 0.3 to about 0.9 AU, using Helios 2 spacecraft measurements in the fast solar wind. The time resolution of the magnetic field data allows us to study the power spectra up to 2 Hz. Generally, the corresponding spectral break frequency f{sub b} and the Doppler-shifted frequencies, which are related to the proton gyroradius and inertial scales, are close to a frequency f of about 0.5 Hz at a distance of 1 AU from the Sun. However, studying the radial evolution of the power spectra offers us the possibility to distinguish between those scales. Recent Ulysses observations show that, while the proton scales vary, f{sub b} stays nearly constant with the heliocentric distance R. In our study we confirm that f{sub b} varies within a small interval of [0.2, 0.4] Hz only, as R varies from 0.3 to 0.9 AU. Moreover, if we assume parallel propagating fluctuations (with respect to the solar wind flow or background magnetic field), we can show that none of the proton scales are coincident with the break scale. If, however, we take into account the two-dimensional nature of the turbulent fluctuations, then we can show that the spatial scale corresponding to f{sub b} (R) does follow the proton inertial scale, {lambda}{sub p}(R), but not the proton gyroradius scale, {rho}{sub p}(R), as a function of heliocentric distance. These observations indicate that the spectral break at the proton inertial scale might be related to the Hall effect, or be controlled by the ion-cyclotron damping of obliquely propagating fluctuations or the formation of current sheets scaling like {lambda}{sub p}, which could be responsible for ion heating through magnetic reconnection.},
doi = {10.1088/0004-637X/749/2/102},
url = {https://www.osti.gov/biblio/22020436}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 749,
place = {United States},
year = {Fri Apr 20 00:00:00 EDT 2012},
month = {Fri Apr 20 00:00:00 EDT 2012}
}